The invention relates to a deposition system, and in particular to a deposition system and film thickness monitoring device thereof.
Due to rapid development in optical industries in recent years, high performance of optical elements is required. Thus, optical deposition accuracy of the optical elements is strictly controlled such that a film thickness monitoring device is often utilized to monitor film thickness during optical deposition process.
Conventional film thickness monitoring devices can be categorized into reflection and transmission monitoring types. FIG. 1A shows a reflection monitoring device 100. When a laser light source 102 emits a light beam onto an optical thin film 106 on an optical substrate 104, a portion of the light is reflected and received by a light receiver 108, measuring thickness of the optical thin film. As shown in FIG. 1A, since the laser light source 102 and light receiver 108 are disposed on the same side of the optical substrate 104, a volume of the reflection monitoring device 100 is reduced and the reflection monitoring device 100 can be disposed on an exterior side of a vacuum chamber of a sputtering coater for film deposition for easy installation and repair. Since film thickness is measured from the reflected light, however, if the substrate is inclined, the reflected light may deviate from the receiving range of the light receiver 108, such that installation and angle calibration of the optical substrate 104 are sensitive. Particularly, design of the optical deposition machine can contain hundreds of optical substrates, such that it is difficult to measure each optical substrate thereof.
FIG. 1B shows a transmission monitoring device 200. The laser light source 202 and the light receiver 202 are disposed on two sides of the optical substrate 204, respectively, such that the light receiver 208 receives laser light beam passing through the optical thin film 206, to prevent light deviation due to inclination of the optical substrate. The arrangement of the laser light source 202 and the light receiver 202 on both sides of the optical substrate 204 increases the total volume of the machine and is difficult to install.